Telephone number verification (or validation) services are online services used to establish whether a given telephone number is in service. They may include a form of Turing test to further determine if a human answers or answering equipment such as a modem, fax, voice mMail or answering machine. Purpose Verification services are often used to limit sockpuppetry, underage sign-ups, spamming and illegal activities like harassment, scams and fraud. Operators and their clients include: Lead generation companies Social networking sites Internet forums dating sites and wikis Any verification operation which sells sets of contact numbers generated through its marketing operations will gain a premium for an efficient list of “clean” numbers. Call center outbound telephone campaigns save time and resources bypassing undefined or mechanized equipment numbers. Telephone numbers entered into an online sign-up form can be checked in real time, by implementing AJAX (background web page processing) type call to a telephone number verification service while the form is still being filled in. To thwart fraud, it is possible to match an online customer to the telephone number owner, to certify it is in fact the same person who owns it. This service is of increasing value to online store managers, banks and credit card processors, who are faced with increasing quantities of attempts to make fraudulent purchases such as by those using stolen credit card details. Methods employed Line test An aborted call is made to the subscriber line. This automated service “listens” to check for ringback tones, busy signals, answered call, voice mail automated answering, or network operator injected messages such as “the number called is not in service”. This method benefits from being international and covering mobile phones. However, the check can take up to 30 seconds to complete (average time 9 seconds). This delay can be handled well by the use of AJAX background processes for example by allowing the user to continue filling in other fields in a form while the line test is performed. Turing test It is possible to employ such methods further to verify that genuine people answer the telephone at that number by requesting a key press tone "Press one to 'unsubscribe'." Often this method is used to clean lists, and rather than unsubscribing, the number is categorized as a live one. Line test + authentication To verify that a telephone number exists and authorize its use, subscribers supply a telephone number